As is well known, a well must always be filled with fluid during drilling. These fluids are referred to as “drilling muds” in that they have special characteristics and are of major importance during the entire drilling process. In effect, it is known that the hydrostatic pressure, through the drilling mud, creates a drive towards the well walls that prevents collapses or falls. This hydraulic action also results in the formation of water-proof plasters in high porosity areas, removing undesirable volume and level losses, and also mitigating the occurrence of spontaneous upwelling springs.
Also, these muds are useful for lubricating and refrigerating the drill bit and the tube column. In addition, when this fluid circulates during drilling, in its way up the well/drilling column annular space, it carries over detritus produced by the action of the drill bit and deposits them on the surface. On the other hand, its great gelation capacity prevents solid particles from falling over the drill bit and undesirable blocking and clogging when circulation must be interrupted for any reason. In bottom engine drilling systems, mud is responsible for transmitting the hydraulic energy necessary to drive the hydraulic engine and the drill bit. The mud is even used to transmit signals that allow tool remote control. Controlling and managing the parameters of this fluid allow for controlling of the development of operations, and to that end, it is of paramount importance to permanently maintain the continuity of the injection circuit.
In the event of contingencies, such as circulation losses caused by the admission of permeating layers, or appearance of layers with high reservoir pressure, or even the blockage of the tube column with the ring blockage, etc, when the mud injection circuit is active, the problem is generally readily solved by changing the mud parameters and the hydraulic conditions, without requiring to interrupt circulation.
However, if the contingency occurs while the circulation circuit is open or discontinued, the time required for its start-up is highly critical, and the ensuing problems typically require additional high risk/cost tasks.
In effect, as is well known, it is after the drilling and assessment of the well that the tubing job is performed. The aim is to install a pipe column of special strength and structure to supply the well with the necessary stability for post-exploitation tasks.
This installation operation is currently performed with the pipe open, on a pipe per pipe basis, which are joined by threading. The well is kept open for the duration of the tubing operation, and the mud circuit is discontinued.
As indicated above, it is desirable that, during tubing, the drilling fluid should be circulated from the deposit pools to the inside of the pipe, from its lower end to the well-pipe annular space and from the latter to the mud pools, to be re-pumped.
The purpose is that the fluid move forward through the mentioned annular space, so as to fill, wash or condition the well-pipe annular space at different depths.
The fact is that in order to complete the aforementioned circuit, the circulation head must be assembled during tubing.
This is not a complicated task under normal operating conditions, in which case the necessary assemblies can be done quickly and the required time is not critical.
But in the event of any contingencies, such as the blockage of the pipe at any lower section, so that the open upper end, where the circulation head must be threaded, is far from the work floor, installation turns considerably difficult, and contingent risks increase.
It is also known that, in addition to pipe blockage, the incorporation of fluid that produces a weak layer decreases the level and results in differential pressure loss over strong layers, increasing the possibility of spring occurrences.
Evidently, as no drilling mud circulates through the circuit, there will be clogging and/or well shutdown due to solid deposits. It is therefore crucial to avoid delays under these circumstances.
Indeed, isolation cementation is of paramount importance in the construction of oilfield wells since the productive life of the well depends on its result.
If the cementation if flawed, it is more difficult to obtain accurate assessments that might lead to the abandonment of the well, and even of the field when the latter is exploratory.
Isolation cementation is the last phase in the drilling of an oil well. After drilling and tubing, the mentioned created annular space must be cemented.
This important operational stage is called “primary or isolation cementation” because the injected cement must fill the whole existing annular space defined between the well itself and the pipe external wall with which it is tubed to isolate the layers from one another and to affix the pipe to the assembly.
It is known that, in order to achieve effective cementation, it is necessary to prepare the well and pipe walls, ensuring that the cement that is to be injected, after hardening, has good adhesion properties, both to the pipe and the assembly, without creating undesirable interstices that might affect the perfect isolation required.
The preparation for the mentioned annular space is provided by the water cushions that are injected before the main cementing slurry.
That means that after tubing and before starting cementation, in normal conditions, the pipe and the well are filled with drilling fluid. To cement, it is previously necessary to wash the inside of the pipe to avoid the contamination of the cement fluids.
These fluids, which are injected through the inside of the pipe towards its lower end and then move up the well-pipe annular space, are: the water cushion, the removing slurry and the main or cementing slurry itself.
The separation or removal of the drilling fluid from the pipe inside is provided by a first lower plug, usually called a “fuse plug” that is located and acts before the mentioned cushions. The cement head is essentially a lower plug bearing device as well as an upper block plug bearing device, which will be launched eventually to implement the aforementioned task, that is, to prepare the annular space and then inject the water cushion and the removing and main slurries.
In known installations, the cement head must be attached to the tubing pipe through the threaded joint offered by the last coupling, and must also become integrated into the fluid injection circuit by means of a communications pair, namely: one disposed over the lower fuse plug, and the other, over the upper plug.
It is common for these derivations from the main injection circuit to include selective valves that first direct fluid circulation towards the lower fuse plug that is displaced to the lower drilling end through the pumping of the mentioned cushion and slurry.
Then, the same selective valves switch position so that the displacement fluid can be introduced over the upper block plug that presses the mentioned cement fluids contained between both plugs.
The generated hydraulic pressure causes the breakage of the fuse plug located at the pipe lower end (the fuse membrane bursts), so that the mentioned fluids contained between them are displaced from the inside of the pipe to the well-pipe annular space.
Since the mentioned displacement fluid injected behind the upper or block plug pushes the latter until it reaches the fuse plug, it can be inferred that, at that time, all the cement fluid volume is occupying said well-pipe annular space.
After hardening, the cement will isolate the productive and non-productive layers from one another and will maintain the pipe stable and fixed to the assembly.
The cement heads currently known in the art adequately perform the process explained above and can satisfy the operational requirements presented because each of the plugs can be launched at the corresponding time.
However, it is always necessary to have two inlets or connections with the fluid feed circuit to ensure that no air reaches the inside.
In all cases, the presence of operators is required at the wellhead, with the risks involved in working with the pressurized circuit.
The most modern cementation equipment includes up to three connections with the fluid inlet and two or three special compartments designed place the standby plugs until the moment of their launching.
They are very simple, effective, and easy to operate devices, but all of them are designed to be installed at the time of cementation.
Their collocation is performed once tubing is completed and after the mentioned previous drilling fluid circulation for the cleansing and conditioning of the well and the pipe.
These heads are mounted on the last pipe coupling, allowing the introduction of the mentioned cement plugs.
The most remarkable problem arising is that the fluid supply must invariably be discontinued and the circuit must be shut down in order to mount the cement head.
This is a manual mounting operation that requires the shutdown of the feed circuit, the installation of the cement head and its connections, and the installation of the plugs, after completing the tubing.
The time required by these tasks is crucial and it has been long determined that it is at this stage that contingencies are produced.
These devices invariably require the presence of operators at the wellhead to install the cement head, so that, once the latter has been installed, they can open the corresponding valves for the launching of the plugs.
This post-tubing assembly prevents the use of remote controls, which are extremely useful in centralizing operational controls, and the plug launching operation is not plotted in any graph. In this sense, it should be highlighted, for instance, that the valve change required to launch the block plug, the depression produced by the free-falling cement creates an undesirable entry of air to the circuit, that later makes flow and pressure readings more difficult, with undesirable volume returns after arrival of the block plug due to the compression of the confined air, which forces to keep the cement head closed.
This action later produces a volume increase due to the heating of the displaced fluid, contained inside the tubed pipe, which expands the latter while the cement is hardening.
When said pipe decompresses to perform the tasks subsequent to well finishing, a micro annular space is formed between the outer pipe wall and the body of the hardened cement that creates a communication between the layers, which may cause problems that might require highly complicated and costly supplementary repair works.
With respect to the self-adjustable annular seal used to contain the pressures generated from the well, it can be said that a considerable number of checks and elastic joints that serve as fluid retention devices, whether pressurized or not, in hydraulic or pneumatic mechanisms. The most used devices are the elastic toroidal joints commonly known as “O-rings”. They are placed in an annular encasement or throat which size and format are usually determined by standards established by the manufacturer itself.
When the pressure affects one of the seal faces, the confinement by contact with the encasement bottom and the surface to be sealed, it pushes the sealing ring towards the back wall or bottom of said encasement; consequently, the elastic ring is deformed in the space between the axis and the bushing, efficiently closing the way to pressure.
The mechanical retention capacity of this type of joint is determined by the quality of the elastomer it is made of, based on its resistance to temperature and chemicals, hardness, machinery tolerance, etc.
Another known sealing means is the one known as “V” or “Multi V” type. These seals are not typically built with pure elastomers; they are semi-rigid and are characterized by their special shape, since they feature wings that are adjusted on the wall of the encasement bottom, so that the pressure in this case affects the inside of the wings, pushing them towards the walls to be sealed.
These seals are generally used to withstand high pressures and axial or rotational movements. Said sealing elements with “V” lips, combined with “O” rings, are commonly used to seal larger spaces and less polished surfaces.
The physical and chemical characteristics of the compounds with which these seals are built are directly related to the intended mechanical response, and to the environment to which they will be exposed.
With respect to the so called elastic checks, they generally combine a metallic structure associated to an elastomer. They are commonly used to contain fluids over rotational movements, are not capable of containing high pressures.
The self-adjustable annular ring used by the tool of the invention features considerable differences over the typical models currently in use, in that the expansible chamber connected to the contained pressure provides an additional automatic adjustment, which can be useful to perform a regulating blockage action, which, in addition to the natural elastic capability of the contact lips, increases the blockage and/or restraint action on the surface to be sealed, directly related to the tolerated pressure.
It is precisely called “dynamic pressure self-adjustable annular seal” because the blockage action increases or decreases with the increase or decrease of the pressure of the fluid contained by means of the seal.
It is a hermetic sealing means that can be used in hydraulic and/or pneumatic mechanisms, in static and/or dynamic mechanisms, sealing and/or outer blocking an axis.
This functional principle increases the blockage pressure, using the contained fluid's own pressure.